Anti-fuse device structure and electroplating circuit structure and method

ABSTRACT

Disclosed are embodiments of a circuit and method for electroplating a feature (e.g., a BEOL anti-fuse device) onto a wafer. The embodiments eliminate the use of a seed layer and, thereby, minimize subsequent processing steps (e.g., etching or chemical mechanical polishing (CMP)). Specifically, the embodiments allow for selective electroplating metal or alloy materials onto an exposed portion of a metal layer in a trench on the front side of a substrate. This is accomplished by providing a unique wafer structure that allows a current path to be established from a power supply through a back side contact and in-substrate electrical connector to the metal layer. During electrodeposition, current flow through the current path can be selectively controlled. Additionally, if the electroplated feature is an anti-fuse device, current flow through this current path can also be selectively controlled in order to program the anti-fuse device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No. 12/031,761filed Feb. 15, 2008, U.S. Pat. No. 7,935,621, issued on May 3, 2011, thecomplete disclosure of which, in its entirety, is herein incorporated byreference.

FIELD OF THE INVENTION

The embodiments of the invention generally relate electroplatingfeatures onto a semiconductor wafer and, more particularly, to ananti-fuse device structure and a circuit and method for electroplatingas well as programming the anti-fuse device structure.

BACKGROUND Description of the Related Art

An electroplating circuit typically includes an anode (i.e., a source ofmetal or alloy), a cathode (i.e., an item to be electroplated with themetal or alloy), an electroplating bath for holding an electroplatingsolution into which the anode and cathode are submerged and an externalpower supply connected to the anode and cathode to provide a currentflow through the circuit. Specifically, the current flow and, thereby,electron flow will cause metal ions in the electroplating solution tolose their charge and plate onto the cathode. This current flow willfurther cause the anode to replenish the metal ions in the solution.

Electroplating (i.e., electrodeposition) is often used to form back endof the line (BEOL) features, such as wires, metal-insulator-metaldevices, capacitors, etc., on a semiconductor wafer. For example, asdescribed in “Damascene copper electroplating for chip interconnections”by Andricacos et. al, IBM Journal of Research and Development, Vol. 42,No. 5, 1998, various techniques can be used for forming a BEOLelectroplated feature on a semiconductor wafer. One technique involvesforming a seed layer (i.e., a thinly deposited conductive layer) on thewafer. Next, a mask is formed on the seed layer such that only thatportion of the seed layer to be plated is exposed. A contact at thewafer edge conducts current through the seed layer duringelectroplating. Once the electroplating process is completed, the masklayer is removed, followed by removal of any exposed seed layer. Anothertechnique involves forming a single-tier trench for metal lines only ora double-tier trench for metal lines and via holes. Next, a blanketbarrier layer and blanket conductive seed layer are formed. A contact atthe wafer edge conducts current through the seed layer duringelectroplating. Once the electroplating process is completed, achemical-mechanical polishing (CMP) process is used to remove barriermaterial, seed material and electroplating material outside the trench.

As mentioned above, each of these techniques requires the use of acontacted seed layer (i.e., a thinly deposited conductive layer) toprovide a current path from the power supply to the cathode (i.e., fromthe power supply to the area of the wafer that is to be electroplated).In the former technique, once the electroplating process is complete,additional process steps are required to remove the mask and any excessseed layer that was not electroplated. In the latter technique, once theelectroplating process is complete, additional process steps arerequired to remove any excess seed layer, barrier layer andelectroplated material outside the trench. These additional processingsteps increase manufacturing costs and time. Consequently, there is aneed in the art for an electroplating circuit and an electroplatingmethod, which eliminates the need to use a seed layer and whichminimizes the number of subsequent processing steps.

SUMMARY

In view of the foregoing, disclosed herein are embodiments of a circuitand method for electroplating a feature, such as a back end of the line(BEOL) anti-fuse device, onto a semiconductor wafer. The electroplatingcircuit and method embodiments eliminate the use of a seed layer and,thereby, minimize subsequent processing steps. Specifically, the circuitand method embodiments allow for selective electroplating of one or moremetal or alloy materials onto an exposed portion of a metal layer in atrench on the front side of a semiconductor substrate. This isaccomplished by providing a unique wafer structure that allows a currentpath to be established from a power supply through a back side contactand in-substrate electrical connector to the metal layer. Duringelectrodeposition, current flow and, thereby, electron flow, through thecurrent path can be selectively controlled. Additionally, if theelectroplated feature is an anti-fuse device, current flow through thiscurrent path can also be selectively controlled in order to program theanti-fuse device.

More particularly, disclosed herein are embodiments of a circuit forelectroplating a feature (e.g., a back end of the line (BEOL) conductor,insulator, metal-insulator-metal (MIM) structure, capacitor, etc.) ontoa semiconductor wafer. As with known electroplating circuits used forelectroplating such features onto a semiconductor wafer, the circuitembodiments of the present invention can comprise a wafer, anelectroplating solution in an electroplating bath, an anode submerged inthe electroplating solution, an external power supply electricallyconnected to the anode, and an electroplating rack for holding the wafersubmerged in the electroplating solution as well as for electricallyconnecting the wafer to the external power supply. However, in thecircuit embodiments of the present invention, the wafer is configureddifferently than wafers used in prior art electroplating circuits sothat a seed layer is not required for electrodeposition.

Specifically, the wafer can comprise a substrate with a front side and aback side. At least one metal layer can be positioned on the front sideof the substrate and a dielectric layer can be positioned on the metallayer. A trench (e.g., a via hole, a contact hole, etc.) can extendthrough the dielectric layer such that a portion of the metal layer isexposed. Thus, the entire bottom surface of the trench comprises anexposed portion of the metal layer and, more particularly, comprises thecathode onto which the feature will be electroplated. No seed layer isrequired on the front side of the wafer or within the trench.

The wafer can further comprise a back side contact. Specifically, thiscontact can be positioned within and at the back side of the substrate.The external power supply can be electrically connected to the waferthrough this back side contact. For example, the wafer can be placed inthe electroplating rack such that the back side contact is electricallyconnected to the rack and, thereby, electrically connected to theexternal power supply.

Additionally, the wafer can comprise an in-substrate electricalconnector. Specifically, this electrical connector can be positionedwithin the substrate between the contact and the metal layer. Thiselectrical connector can be adapted to provide an electrical connectionbetween the contact and the metal layer such that a current path isestablished from the power supply through the rack, through the backside contact, through the electrical connector and through the metallayer to the bottom surface of the trench.

The power supply can be adapted to pass a flow of current through thiscurrent path and either the electrical connector or the power supplyitself can be adapted to selectively control the current flow. Forexample, the electrical connector can comprise a switch (e.g., a fieldeffect transistor (FET), a diode, etc.) within the substrate thatelectrically connects the contact to the metal layer. This switch can beadapted to selectively control the current flow between the contact andthe metal layer. Alternatively, the electrical connector can comprise asimple ohmic path within the substrate that electrically connects thecontact and the metal layer. Current flow through this simple ohmic pathcan be selectively controlled by the external power supply itself.

During operation of the electroplating circuit, selective control ofcurrent flow through the current path between the power supply and themetal layer and, more particularly, between the power supply and theexposed portion of the metal layer at the bottom surface of the trench(i.e., between the power supply and the cathode) allows for selectivecontrol of electron flow. As discussed above, when the wafer issubmerged in an electroplating solution in an electroplating bath, alongwith an anode, electron flow to the exposed portion of the metal layerat the bottom of the trench (i.e., to the cathode) will cause the metalor alloy ions in the electroplating solution to lose their charge and toplate onto the bottom surface of the trench.

In one particular embodiment, this electroplating circuit can be used toform one or more anti-fuse layers of a BEOL in-via hole or in-contacthole anti-fuse device on the semiconductor wafer and further can be usedwhen programming such a BEOL anti-fuse device. More specifically, a BEOLanti-fuse device, formed using the above-described circuit, can comprisea plurality of anti-fuse layers. For example, the BEOL anti-fuse devicecan comprise a first anti-fuse layer on the bottom surface of thetrench, a second anti-fuse layer on the first anti-fuse layer, and athird anti-fuse layer on the second anti-fuse layer. At least one ofthese anti-fuse layers can comprise electroplated layers (e.g., thefirst, second and, optionally, the third anti-fuse layers can beelectroplated using the above described circuit).

As with conventional anti-fuse devices, the first and third anti-fuselayers can comprise layers of conductive materials (i.e., conductiveplates) and the second anti-fuse layer can comprise a thin layer (e.g.,approximately 100-500 angstroms) of dielectric material. In an exemplaryconfiguration, the BEOL anti-fuse device can comprise a first anti-fuselayer comprising titanium nitride (TiN), a second anti-fuse layercomprising silicon dioxide (SiO₂) and a third anti-fuse layer comprisingcopper. However, alternative anti-fuse elements can include, but are notlimited to, nickel (Ni), titanium (Ti), cobalt (Co), iron (Fe), copper(Cu), platinum (Pt), rhenium (Re) or ruthenium (Ru).

As discussed above, during operation of the circuit to electroplate afeature onto a semiconductor wafer and in this case to electroplate atleast one of the anti-fuse layers of a BEOL anti-fuse device onto thebottom surface of a trench, the unique wafer structure allows forselective control of current flow through a current path between thepower supply and the bottom surface of the trench onto which theanti-fuse layers are being electroplated. Since the wafer structureallows for selective control of current flow through the current pathduring operation of the circuit, it can further provide a means by whichthe anti-fuse device can subsequently be programmed. That is, a currentabove a specified limit can be applied to the first anti-fuse layer atthe bottom of the trench via the previously established current path,thereby, causing metal ions to migrate into the second anti-fuse layerand reducing the resistance across the anti-fuse device (i.e., thereby,programming the anti-fuse device).

Also disclosed herein are embodiments of a method for electroplating afeature (e.g., a back end of the line (BEOL) conductor, insulator,metal-insulator-metal (MIM) structure, capacitor, etc.) onto asemiconductor wafer. As with known electroplating methods, the methodembodiments of the present invention can comprise providing a wafer,providing an electroplating bath containing an electroplating solution,providing an anode submerged in the electroplating solution, providingan external power supply electrically connected to the anode, andproviding a rack for electrically connecting the external power supplyto the wafer and for holding the wafer submerged in the electroplatingsolution of the electroplating bath. However, in the method embodimentsof the present invention the wafer is uniquely processed so that a seedlayer is not required for electrodeposition.

Specifically, the method embodiments of the present invention compriseproviding a wafer having a semiconductor substrate with a front side anda back side. During front end of the line (FEOL) processing of thewafer, a contact can be formed within and at the back side of thesubstrate. Next, an electrical connector can be formed within thesubstrate such that it is adjacent to and, more particularly,electrically connected to the back side contact.

The process of forming this electrical connector can comprise forming aswitch (e.g., a field effect transistor, diode or any other suitablesemiconductor switch) within the semiconductor substrate adjacent to theback side contact. Alternatively, the process of forming this electricalconnector can comprise forming a simple ohmic path within the substrateadjacent to the back side contact.

Then, during back end of the line (BEOL) processing, at least one metallayer can be formed on the front side of the substrate adjacent to thein-substrate electrical connector. Specifically, during BEOL processing,interlayer dielectric and metal layers can be formed in an alternatingpattern above the front side of the substrate and, more particularly, onthe front side of the substrate above the in-substrate electricalconnector (i.e., above the switch or simple ohmic path). As theinterlayer dielectric and metal layers are formed, one or more viainterconnects are formed in order to electrically connect thein-substrate electrical connector (i.e., the in-substrate switch orsimple ohmic path) to the top metal layer of the pattern.

Next, a dielectric layer is formed on the top metal layer and a trench(e.g., a via hole, a contact hole, etc.) is formed through thedielectric layer in order to expose a portion of this top metal layer atthe bottom surface of the trench. It should be noted that reference totop and bottom are somewhat arbitrary and are defined by the directionon the current flow during plating. Then, a feature is formed in thistrench and, more particularly, a feature is formed on the exposedportion of the metal layer on the bottom surface of the trench. In orderto form this feature, one or more electrodeposition processes areperformed.

Specifically, a power supply is electrically connected to an anode andan electroplating rack. The wafer is placed in the electroplating racksuch that the rack is electrically connected to the back side contact.Thus, a current path is established from the power supply through therack, through the back side contact, the electrical connector,optionally through one or more vias and/or intermediate metal layers,through the top metal layer to the exposed portion of the top metallayer at the bottom surface of the trench (i.e., to the cathode). Then,the anode and the rack with the wafer are both submerged in theelectroplating solution of the electroplating bath. Next, current flowfrom the power supply through the current path is selectively controlled(e.g., by either the optional switch or the power supply itself).Selective control of current flow and, thereby, electron flow throughthe current path between the power supply and the exposed portion of themetal layer at the bottom surface of the trench (i.e., between the powersupply and the cathode) causes metal or alloy ions in the electroplatingsolution to lose their charge and to plate onto the bottom surface ofthe trench (i.e., to plate onto the cathode). This process can berepeated to create different layers of electroplated material within thetrench.

Thus, the electroplating method, discussed above, can be used toelectroplate any number of various different types of features onto thesemiconductor wafer, including but not limited to, back end of the line(BEOL) conductors, insulators, metal-insulator-metal (MIM) structures,capacitors, anti-fuse devices, etc. In one particular embodiment, thiselectroplating method can be used when forming one or more anti-fuselayers of a BEOL in-via hole or in-contact hole anti-fuse device andfurther can be used when programming such a BEOL anti-fuse device.

More specifically, the BEOL anti-fuse device, discussed above, can beformed by electroplating a plurality of anti-fuse layers within a trench(i.e., within in a BEOL via or contact hole). To accomplish this, thewafer is processed, as described above. That is, a contact is formedwithin and at the back side of the wafer substrate. An electricalconnector is formed within the substrate adjacent to the contact. Ametal layer is formed on the front side of the substrate adjacent to theelectrical connector. A dielectric layer is formed on the metal layer. Atrench is formed in the dielectric layer so as to expose a portion ofthe metal layer at the bottom surface of the trench.

Then, the contact is electrically connected to the power supply suchthat a current path is established from the power supply through thecontact and the electrical connector to the metal layer and, moreparticularly, to the exposed portion of the metal layer at the bottomsurface of the trench (i.e., the cathode). This can be accomplished, forexample, by electrically connecting an electroplating rack to powersupply and then placing the wafer in the electroplating rack such thatthe back side contact is electrically connected to the electroplatingrack.

Next, a first electrodeposition process can be performed. This firstelectrodeposition process can comprise electrically connecting the powersupply to an anode. Then, the electroplating rack with the wafer and theanode are submerged in a first electroplating solution in theelectroplating to a power supply such that the bottom surface of thetrench is exposed to the first electroplating solution. During thisfirst electrodepositing process, current flow and, thereby, electronflow, through the current path is selectively controlled (e.g., byeither the in-substrate switch or the power supply itself) so as toelectroplate a first anti-fuse layer onto the bottom surface of thetrench.

After the first anti-fuse layer is plated onto the bottom surface of thetrench, a second electrodepostion process can be performed. This secondelectrodeposition process can comprise replacing the firstelectroplating solution in the electroplating bath with a secondelectroplating solution and submerging the rack with the wafer in thesecond electroplating solution such that the first anti-fuse layer isexposed to the second electroplating solution. During this secondelectrodeposition process, current flow and, thereby, electron flowthrough the current path is selectively controlled (e.g., by either thein-substrate switch or the power supply itself) so as to electroplate asecond anti-fuse layer onto the first anti-fuse layer in the trench.

After the second anti-fuse layer is plated onto the second anti-fuselayer, a third electrodepositon processes can be performed. This thirdelectrodeposition process can comprise replacing the secondelectroplating solution in the electroplating bath with a thirdelectroplating solution and submerging the rack with the wafer in thethird electroplating solution such that the second anti-fuse layer isexposed to the third electroplating solution. As with the previouslydescribed electrodeposition processes, during this thirdelectrodeposition process, current flow and, thereby, electron flowthrough the current path can be selectively controlled (e.g., by eitherthe in-substrate switch or the power supply itself) so as toelectroplate a third anti-fuse layer onto the second anti-fuse layer inthe trench.

Alternatively, after the second anti-fuse layer is plated onto thesecond anti-fuse layer, a third anti-fuse layer can be formed on thesecond anti-fuse layer in the via/contact hole simultaneously withforming at least one standard via interconnect/contact on the wafer,using-well known standard deposition techniques.

Once the BEOL anti-fuse device is formed and BEOL wafer processing iscompleted, the BEOL anti-fuse device can be programmed by selectivelycontrolling current flow through the current path in the same mannerdescribed above for electrodeposition. That is, a current path can beestablished from a power supply through the back side contact, throughthe electrical connector, through the metal layer to the BEOL anti-fusedevice within the trench. Then, current flow through this current pathcan be selectively controlled (e.g., by either the switch or the powersupply itself, depending upon the wafer structure) in order to apply acurrent above a specified limit to the anti-fuse device and, moreparticularly, to the first anti-fuse layer of the anti-fuse deviceadjacent to the bottom surface of the trench. This applied current willcause metal ions to migrate into the second anti-fuse layer, thereby,reducing resistance across the anti-fuse device (i.e., thereby,programming the anti-fuse device).

These and other aspects of the embodiments of the invention will bebetter appreciated and understood when considered in conjunction withthe following description and the accompanying drawings. It should beunderstood, however, that the following descriptions, while indicatingembodiments of the invention and numerous specific details thereof, aregiven by way of illustration and not of limitation. Many changes andmodifications may be made within the scope of the embodiments withoutdeparting from the spirit thereof, and the embodiments of the inventioninclude all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention will be better understood from thefollowing detailed description with reference to the drawings, in which:

FIG. 1 is a diagram of an electroplating circuit for a semiconductorwafer;

FIG. 2 is a diagram of an embodiment of an electroplating circuit for asemiconductor wafer according to the present invention;

FIG. 3 a is cross-section diagram of a semiconductor wafer with a backside contact and in-substrate electrical connector (e.g., a switch orsimple ohmic path) that may be incorporated into the electroplatingcircuit of FIG. 2;

FIG. 3 b is a schematic diagram of the electroplating circuit of FIG. 2incorporating the semiconductor wafer of FIG. 3 a;

FIG. 4 a is a cross-section diagram of a semiconductor wafer with a backside contact and in-substrate transistor-type switch that may beincorporated into the electroplating circuit of FIG. 2;

FIG. 4 b is a schematic diagram of the electroplating circuit of FIG. 2incorporating the semiconductor wafer of FIG. 4 a;

FIG. 5 a is a cross-section diagram of a semiconductor wafer with a backside contact and in-substrate diode-type switch that may be incorporatedinto the electroplating circuit of FIG. 2;

FIG. 5 b is a schematic diagram of the electroplating circuit of FIG. 2incorporating the semiconductor wafer of FIG. 5 a;

FIG. 6 is a schematic diagram of the electroplating circuit of FIG. 2incorporating a semiconductor wafer with a back side contact andin-substrate simple ohmic path;

FIG. 7 is a cross-section diagram of a semiconductor wafer having anexemplary BEOL anti-fuse device with at least one anti-fuse layerelectroplated using the circuit of FIG. 2;

FIG. 8 is a schematic diagram illustrating a programming circuit for theBEOL anti-fuse device of FIG. 5;

FIG. 9 is a flow diagram illustrating an embodiment of an electroplatingmethod according to the present invention;

FIG. 10 is a flow diagram illustrating an embodiment of the method ofFIG. 9 used particularly for forming the BEOL anti-fuse device of FIG. 7and for programming that BEOL anti-fuse device; and

FIG. 11 is a cross-section diagram of a partially completed BEOLanti-fuse device;

FIG. 12 is a cross-section diagram of a partially completed BEOLanti-fuse device;

FIG. 13 is a cross-section diagram a partially completed BEOL anti-fusedevice;

FIG. 14 is a cross-section diagram a partially completed BEOL anti-fusedevice;

FIG. 15 is a cross-section diagram of a partially completed BEOLanti-fuse device;

FIG. 16 is a cross-section diagram of a partially completed BEOLanti-fuse device;

FIG. 17 is a cross-section diagram of a completed BEOL anti-fuse device;

FIG. 18 is a cross-section diagram of a partially completed BEOLanti-fuse device; and

FIG. 19 is a cross-section diagram of a completed BEOL anti-fuse device.

DETAILED DESCRIPTION OF EMBODIMENTS

The embodiments of the invention and the various features andadvantageous details thereof are explained more fully with reference tothe non-limiting embodiments that are illustrated in the accompanyingdrawings and detailed in the following description. It should be notedthat the features illustrated in the drawings are not necessarily drawnto scale. Descriptions of well-known components and processingtechniques are omitted so as to not unnecessarily obscure theembodiments of the invention. The examples used herein are intendedmerely to facilitate an understanding of ways in which the embodimentsof the invention may be practiced and to further enable those of skillin the art to practice the embodiments of the invention. Accordingly,the examples should not be construed as limiting the scope of theembodiments of the invention.

As discussed above, electroplating (i.e., electrodeposition) is oftenused to form features, such as wires, metal-insulator-metal devices,capacitors, etc., on a semiconductor wafer. Referring to FIG. 1, anexemplary electroplating circuit 100 for electroplating such features ona semiconductor wafer 125 typically includes an anode 110 (i.e., asource of metal or alloy), a cathode 120 (i.e., the portion of thesemiconductor wafer 125 to be electroplated with the metal or alloy), anelectroplating bath 150 for holding the anode 110 and cathode 120submerged in an electroplating solution 160, and an external powersupply 190 (e.g., a battery) electrically connected to the anode 110 andthe cathode 120 in order to provide a current flow through the circuit100. A rack 140 is often used to hold the wafer 125 in theelectroplating solution 160 and to provide the electrical connectionbetween the power supply 190 and the wafer 125. During theelectroplating process, the current flow will cause metal ions (e.g.,Cu++) in the electroplating solution 160 to lose their charge and platean electroplated layer 128 onto the cathode 120 and will further causethe anode 110 to replenish the metal ions in the solution 160.

However, also as discussed above, in order to ensure electron flow fromthe power supply 190 to the portion of the wafer 125 that is to beelectroplated (i.e., to the cathode 120), a seed layer 121 is generallyrequired. A seed layer 121 is a thinly deposited conductive layer thatis formed so that it extends from the area of the wafer requiringplating 120 to the wafer's edge. At the wafer's edge, the seed layer 121is electrically connected (e.g., by conductors 127) to the rack 140 inorder to establish a current path from the power supply 190, through therack 140, through the seed layer 121 to the portion 120 of the wafer tobe electroplated. However, additional processing steps (e.g., removal ofmasks covering portions of the wafer not electroplated, chemicalmechanical processing, etc.) must be formed in conjunction with using aseed layer during electroplating and these processing steps increasemanufacturing costs and time. Consequently, there is a need in the artfor an electroplating circuit and an electroplating method, whicheliminate the need to use a seed layer and which minimize the number ofsubsequent processing steps.

In view of the foregoing, disclosed herein are embodiments of a circuitand method for electroplating a feature, such as a back end of the line(BEOL) anti-fuse device, onto a semiconductor wafer. The electroplatingcircuit and method embodiments eliminate the use of a seed layer and,thereby, minimize subsequent processing steps. Specifically, the circuitand method embodiments allow for selective electroplating of one or moremetal or alloy materials onto an exposed portion of a metal layer in atrench on the front side of a semiconductor substrate. This isaccomplished by providing a unique wafer structure that allows a currentpath to be established from a power supply through a back side contactand in-substrate electrical connector to the metal layer. Duringelectrodeposition, current flow and, thereby, electron flow, through thecurrent path can be selectively controlled. Additionally, if theelectroplated feature is an anti-fuse device, current flow through thiscurrent path can also be selectively controlled in order to program theanti-fuse device.

More particularly, referring to FIG. 2, disclosed herein are embodimentsof a circuit 200 for electroplating a feature (e.g., a back end of theline (BEOL) conductor, insulator, metal-insulator-metal (MIM) structure,capacitor, anti-fuse device, etc.) onto a semiconductor wafer 225. Theelectroplating circuit 200 embodiments can comprise many of the samefeatures as set out in the exemplary electroplating circuit 100 ofFIG. 1. For example, the electroplating circuit 200 can comprise anelectroplating solution 260 in an electroplating bath 250, an anode 210(i.e., a source of metal or alloy, e.g., Copper (Cu)) submerged in theelectroplating solution 260, an external power supply 290 electricallyconnected to the anode 210, and an electroplating rack 240 for holdingthe wafer 225 submerged in the electroplating solution 260 as well asfor electrically connecting the wafer 225 to the external power supply290. However, in the circuit 200 embodiments of the present inventionthe wafer 225 is configured differently so that a seed layer is notrequired for electrodeposition.

Specifically, referring to FIG. 3 a in combination with the circuitdiagram of FIG. 2, the wafer 225 can comprise a substrate 301 (e.g., abulk silicon wafer, a silicon-on-insulator (SOI) wafer, etc.), having afront side 302 and a back side 303. The wafer 225 can further compriseat least one metal layer (see metal layers 311-313) on the front side302 of the substrate 301 and a dielectric layer 315 on the top metallayer 313. A trench 335 (e.g., a via hole, a contact hole, etc.) canextend through the dielectric layer 315 such that a portion of the metallayer 313 is exposed. Thus, the entire bottom surface of the trench 335comprises an exposed portion of the top metal layer 313 and, morespecifically, comprises the cathode 220 (i.e., the portion of the waferto be electroplated).

The wafer 225 can further comprise a back side contact 226.Specifically, this contact 226 can be positioned within and at the backside 303 of the substrate 301. The external power supply 290 can beelectrically connected to the wafer 225 through this back side contact226. For example, the wafer 225 can be placed in the electroplating rack240 such that the back side contact 226 is electrically connected to theelectroplating rack 240 and, thereby, electrically connected to theexternal power supply 290.

Additionally, the wafer 225 can comprise an in-substrate electricalconnector 370. Specifically, this electrical connector 370 can bepositioned within the substrate 301 between the back side contact 226and the metal layer 313. This electrical connector 370 can be adapted toprovide an electrical connection between the contact 226 and the metallayer 313 such that, as illustrated in FIG. 3 b, a current path 385 isestablished from the external power supply 290, through theelectroplating rack 240, through the back side contact 226, through theelectrical connector 370, through interconnects 316 and intermediatemetal layers 311-312, through the top metal layer 313 to the exposedportion of the metal layer at the bottom surface of the trench 335(i.e., to the cathode 220).

The power supply 290 can be adapted to pass a flow of current throughthis current path and either the electrical connector 370 or the powersupply itself can be adapted to selectively control the current flowthrough the current path 385. For example, the in-substrate electricalconnector 370 can comprise a switch (e.g., a field effect transistor(see FIGS. 4 a-4 b), a diode (see FIGS. 5 a-5 b) or any other suitablesemiconductor switch) within the substrate 301 such that it electricallyconnects the contact 226 to the metal layer 313 (e.g., via interconnects316 and intermediate metal layers 311-312). This switch can be adaptedto selectively control the current flow through the path 385 between thecontact 226 and metal layer 313. Alternatively, the electrical connector370 can comprise a simple ohmic path within the substrate 301 thatelectrically connects the contact 226 to the metal layer 313 (e.g., viainterconnects 316 and intermediate metal layers 311-312). Current flowthrough this simple ohmic path can be selectively controlled by theexternal power supply 290 itself.

More specifically, referring to FIG. 4 a in combination with FIG. 2, theelectrical connector 370 can comprise a field effect transistor. Thefirst node 371 (e.g., the drain region) of the field effect transistorcan be electrically connected to the top metal layer 313 (e.g., by meansof one or more via interconnects 316 and one or more intervening metallayers 311-312) and, thereby, electrically connected to the bottomsurface of trench 335 (i.e., electrically connected to the cathode 220).The second node 372 (e.g., the source region) of the field effecttransistor can be electrically connected to the back side contact 226and, thereby, electrically connected to the power supply 290 (e.g.,through rack 240). Finally, the third node 373 (e.g., the gate) of thefield effect transistor can be electrically connected to the powersupply 290 through rack 240 by interconnect 316, metal pad 375 and wire376 that extend to the wafer's edge. Thus, as illustrated in FIG. 4 b,if the electrical connector 370 comprises a field effect transistor,when the wafer 225 is placed in rack 240, a current path 385 isestablished from the external power supply 290, through the rack 240,through the back side contact 226 through the nodes 372-371 of the FET(i.e., of the electrical connector 370) to the exposed portion of themetal layer 313 at the bottom surface of the trench 335 (i.e., to thecathode 220). Current flow and, thereby, electron flow, through thiscurrent path 385 can be selectively controlled depending upon thevoltage applied at gate 373 through wire 376, metal pad 375 andinterconnect 316.

Alternatively, referring to FIG. 5 a in combination with FIG. 2, theelectrical connector 370 can alternatively comprise a diode. The firstnode 371 of the diode can be electrically connected to the top metallayer 313 (e.g., by means of one or more via interconnects 316 and oneor more intervening metal layers 311-312) and, thereby, electricallyconnected to the exposed portion of the metal layer at the bottomsurface of trench 335 (i.e., electrically connected to the cathode 220).The second node 372 of the diode can be electrically connected to theback side contact 226 and, thereby, electrically connected to the powersupply 290 (e.g., through rack 240). Thus, as illustrated in FIG. 5 b,if the electrical connector 370 comprises a diode, when the wafer 225 isplaced in rack 240, a current path 385 is established from the externalpower supply 290, through the rack 240, through the back side contact226 through the nodes 372-371 of the diode (i.e., of the electricalconnector 370) to the exposed portion of the metal layer 313 at thebottom surface of the trench 335 (i.e., to the cathode 220). Currentflow and, thereby, electron flow, through this current path 385 can beselectively controlled depending upon the voltage applied at node 372.

Alternatively, referring to FIG. 6 in combination with FIG. 2, theelectrical connector 370 can comprise a simple ohmic path electricallyconnected between the back side contact 226 and the exposed portion ofthe metal layer 313 at the bottom surface of the trench 335 (i.e., andthe cathode 220). Thus, when the wafer 225 is placed in rack 240, acurrent path 385 is established from the external power supply 290,through the rack 240, through the back side contact 226, through theohmic path (i.e., through the electrical connector 370) to the exposedportion of the metal layer 313 at the bottom surface of the trench 335(i.e., to the cathode 220). Current flow and, thereby, electron flow,through this current path 385 can be selectively controlled by theexternal power supply 290 itself.

Referring again to FIG. 2, during operation of the electroplatingcircuit 200, selective control of current flow through the current path385 (see FIGS. 3 b, 4 b, 5 b and FIG. 6) between the power supply 290and the metal layer 313 and, more particularly between the power supply290 and the exposed portion of the metal layer at the bottom surface ofthe trench (i.e., between the power supply 290 and the cathode 220)allows for selective control of electron flow. As discussed above, whenthe wafer is submerged in an electroplating solution 260 in anelectroplating bath 250, along with an anode, electron flow to thecathode 220 (i.e., to the exposed portion of the metal layer 313 at thebottom surface of the trench 335) will cause metal ions (e.g., Cu++) inthe electroplating solution 260 to lose their charge and plate onto theonto the cathode 220 and will further cause the anode 210 to replenishthe metal ions in the solution 260.

This electroplating circuit 200 can be used to electroplate any numberof various different types of features on the wafer 225, including butnot limited to, back end of the line (BEOL) conductors, insulators,metal-insulator-metal (MIM) structures, capacitors, anti-fuse devices,etc.

For example, referring to FIG. 7 in combination with FIG. 2, in oneparticular embodiment, the electroplating circuit 200 can be used whenforming one or more anti-fuse layers 701-703 of a BEOL in-via hole orin-contact hole anti-fuse device 700 on the semiconductor wafer 225. Theanti-fuse device 700 comprises a plurality of anti-fuse layers 701-703.Theses layer 701-703 can be formed in the trench 335 (e.g., in a backend of the line (BEOL) via hole or contact hole) that extends throughthe dielectric layer 315 to the metal layer 313 and can, moreparticularly, be formed without a seed layer in the via/contact hole.Specifically, this anti-fuse device 700 can comprise a first anti-fuselayer 701 directly adjacent to the exposed portion of the metal layer313 at the bottom surface 220 of the trench. A second anti-fuse layer702 can be positioned on the first anti-fuse layer 701 and a thirdanti-fuse layer 703 can be positioned on the second anti-fuse layer 702.

As with conventional anti-fuse devices, the first and third anti-fuselayers 701 and 703 can comprise layers of conductive materials (i.e.,conductive plates) and the second anti-fuse layer 502 can comprise athin layer (e.g., approximately 100-500 angstroms) of dielectricmaterial. Those skilled in the art will recognize that anti-fuse devices700 perform in a manner opposite that of fuses. That is, a fuse providesa low resistance electrical connection until the fuse is programmed(i.e., blown by allowing a current which exceeds a specified limit toflow through the fuse), at which time the connection is broken.Contrarily, only upon programming (i.e., by applying a current above aspecified limit) does an anti-fuse device 700 provide a low resistanceelectrical connection due to migration of metal ions into the secondanti-fuse layer 702.

In an exemplary configuration, the BEOL anti-fuse device 700 cancomprise a titanium nitride (TiN) layer (i.e., the first anti-fuse layer701) formed, for example, by electrodeposition directly onto the exposedportion of the metal layer 313 at the bottom surface of the trench 335(i.e., directly on the cathode 220). The anti-fuse device 700 canfurther comprise a silicon dioxide (SiO₂) layer (i.e., the secondanti-fuse layer 702) formed, for example, by electrodeposition on thetitanium nitride (TiN) layer. Finally, the anti-fuse device 700 cancomprise a copper (Cu) layer (i.e., a third anti-fuse layer 703) formed,for example, by electrodeposition or by standard via processing on thesilicon dioxide (SiO₂) layer. This configuration has the added benefitof allowing for copper ion (Cu++) assist during subsequent programmingof the anti-fuse device 700. However, alternative anti-fuse elements caninclude, but are not limited to, nickel (Ni), titanium (Ti), cobalt(Co), iron (Fe), copper (Cu), platinum (Pt), rhenium (Re) and ruthenium(Ru).

As discussed in detail above, during operation of the circuit 200 toelectroplate a feature onto a semiconductor wafer and in this case toelectroplate at least one of the anti-fuse layers of a BEOL anti-fusedevice 700 onto the bottom surface of a trench, the unique waferstructure 225 of the present invention allows for selective control ofcurrent flow through a current path between the power supply and thebottom surface of the trench onto which the anti-fuse layers are beingelectroplated. Since the wafer structure 225 allows for selectivecontrol of current flow through the current path during operation of thecircuit 200, it can further provide a means by which the anti-fusedevice can subsequently be programmed.

More specifically, as discussed in detail above, the wafer structure 225comprises a back side contact 226 and in-substrate electrical connector370 (e.g., a switch or simple ohmic path) that can be used to establisha current path 385 in an electroplating circuit 200 from the powersupply 290, through an electroplating rack 240, through the back sidecontact 226, through the electrical connector 370, through the metallayer 313 to the cathode 220 (e.g., see FIGS. 2 and 3 a-3 b). Also, asdiscussed above, current flow through this current path 385 can beselectively controlled, depending upon the embodiment, by either theelectrical connector 370 (e.g., if the electrical connector 370comprises an in-substrate switch, see FIGS. 4 a-b and 5 a-b) or thepower supply 290 itself (e.g., if the electrical connector 370 comprisesa simple ohmic path, see FIG. 6). Selectively controlling current flowthrough the current path 385 allows for electrodeposition of a feature(e.g., an anti-fuse device) into the trench 335.

Additionally, referring to FIG. 8 in combination with FIG. 7, sincecurrent flow to an anti-fuse device 700 is also required for anti-fusedevice programming, selective control of current flow through a similarcurrent path 885 between a power supply 890 and the metal layer 313 and,more particularly between a power supply 890 and the bottom surface ofthe trench adjacent to the first layer 701 of the anti-fuse device 700can provide the means by which the anti-fuse device 700 is programmed.That is, applying a current above a specified limit to the anti-fusedevice 700 and, more particularly, to the first anti-fuse layer 701 ofthe anti-fuse device 700 through a current path 885 (i.e., a currentpath from a power supply 890, through the back side contact 226, throughthe in-substrate electrical connector 370, (optionally) through one ormore interconnects 316 and intermediate metal layers 311-312, throughthe metal layer 313, to the first anti-fuse layer 701) causes metal ionsto migrate into the second anti-fuse layer 702 and, thereby, reducesresistance across the anti-fuse device 700 (i.e. programs the anti-fusedevice). Thus, the wafer 225 structure is also specifically adapted toprovide selective control of current flow to a BEOL anti-fuse device 700during programming.

Referring to FIG. 9 also disclosed herein are embodiments of a methodfor electroplating a feature (e.g., a back end of the line (BEOL)conductor, insulator, metal-insulator-metal (MIM) structure, capacitor,anti-fuse device, etc.) onto a semiconductor wafer. As with knownelectroplating methods, the method embodiments of the present inventioncan comprise providing a wafer 225 having a substrate, providing anelectroplating bath 260 containing an electroplating solution 260,providing an anode 210 submerged in the electroplating solution 260,providing an external power supply 290 electrically connected to theanode 210, and providing an electroplating rack for electricallyconnecting the external power supply 290 to the wafer 225 and forholding the wafer 225 submerged in the electroplating solution 260 inthe electroplating bath (902, see FIG. 2). However, in the methodembodiments of the present invention the wafer 225 is processed so thata seed layer is not required for electrodeposition (904).

Specifically, the method embodiments of the present invention compriseproviding a wafer 225 having a semiconductor substrate 301 with a frontside 302 and a back side 303 (see FIG. 11). The wafer 225 can, forexample, comprise a bulk silicon (Si) wafer or silicon-on-insulator(SOI) wafer.

During front end of the line (FEOL) processing of the wafer 225, acontact 226 can be formed within and at the back side 303 of thesubstrate 301 (905, see FIG. 11).

Next, an electrical connector 370 can be formed within the substrate 301such that it is adjacent to and, more particularly, electricallyconnected to the back side contact 226 (906, see FIG. 11). This processof forming an electrical connector 370 can comprise forming a switch,such as a field effect transistor (see FIG. 4 a), a diode (see FIG. 5 a)or any other suitable semiconductor switch) within the semiconductorsubstrate 301 adjacent to the back side contact 226. Alternatively, theprocess of forming this electrical connector 370 can comprise forming asimple ohmic path within the substrate 301 adjacent to the back sidecontact 226.

Then, during back end of the line (BEOL) processing, at least one metallayer 311-313 (i.e., a wiring level, a metallization layer, etc.) can beformed on the front side 302 of the substrate 301 adjacent to thein-substrate electrical connector 370 (i.e., above the switch or simpleohmic path) (908). Specifically, during BEOL processing, interlayerdielectric layers 317-319 and metal layers 311-313 can be formed in analternating pattern above the front side 302 of the substrate 301 and,more particularly, on the front side 302 of the substrate adjacent tothe in-substrate electrical connector 370. As the interlayer dielectric317-319 and metal layers 311-313 are formed, one or more viainterconnects 316 are form in order to electrically connect thein-substrate electrical connector 370 (i.e., the in-substrate switch orsimple ohmic path) to the top metal layer 313 in the alternatingpattern. More specifically, conventional processing techniques can beused to form interlayer dielectric (ILD) 317-319 and metal layers311-313 in an alternating pattern above the switch 370 (e.g., above afield effect transistor) such that the top layer of the pattern is ametal layer 313. The resulting top metal layer 313 will be the metallayer onto which the feature will be electroplated.

It should be noted that, as the ILD layers 317-319 and metal layers311-313 are formed at process 908, if the electrical connector 370comprises field effect transistor, then the gate 373 of the field effecttransistor is physically wired (e.g., by via interconnect 316) to ametal pad 375 and this metal pad 375 can further be connected to a wire376 that extends to the wafer's edge (see FIG. 4 a). The pad 375 andwire 376 can be formed in one of the metal layers 311-313 above thesubstrate 301 such that they are electrically isolated from portion ofthe top metal layer 313 onto which the electroplated feature will beformed.

Next, dielectric layer 315 is formed (e.g., deposited) on the top metallayer 313 (914, see FIG. 11). Then, a trench 335 (e.g., a via hole, acontact hole, etc.) is formed in the dielectric layer 315 (e.g., usingconventional lithographic patterning and etching techniques) such that aportion (i.e., cathode 220) of the top metal layer 313 is exposed at thebottom surface of the trench (916). That is, the dielectric layer 315 ispatterned and etched so that the resulting trench 335 exposes thatportion of the top metal layer 313 onto which the electroplated featureis subsequently to be formed. The process 916 of forming the trench 335can be performed in conjunction with simultaneously forming one or moreadditional trenches 1100 (e.g., additional via/contact holes) (918, seeFIG. 11).

These additional via/contact holes 1100 can subsequently be used (seeprocess 934, discussed below) to form standard viainterconnects/contacts 1101 (e.g., to metal layer 1102). If additionalvia/contact holes 1100 are formed at process 918, a mask 1200 can beformed (e.g., deposited and lithographically patterned) so as to protectthese additional via/contact holes 1100 during electrodepositon of afeature into the trench 335 (920, See FIG. 12). Those skilled in the artwill recognize that a mask 1200 over an additional via/contact hole 1100would be required to prevent electroplating caused by any current flowto metal layer 1102, during electrodeposition of the feature into thetrench 335. Specifically, if a current path is (not shown) is providedbetween an external power supply and the additional via/contact hole1100 (e.g., by way of the back side contact 226 and electrical connector370 or by some other means), a mask 1200 would be necessary becauseelectrodeposition will occur in the via/contact hole 1200 in thepresence of a current flow.

Then, the desired feature is formed on the exposed portion of the topmetal layer 313 in the trench 335 (i.e., on the cathode 220) (922, seefor example, FIGS. 13-15). In order to form the desired feature, one ormore electrodeposition processes are performed.

Specifically, referring to FIG. 2, a power supply 290 is electricallyconnected to an anode 210 and an electroplating rack 240 (924). Thewafer 225 is then placed in the electroplating rack 240 such that theback side contact 226 and also wire 376 (if the electrical connector 370is an in-substrate field effect transistor, as illustrated in FIG. 4 a)are electrically connected to the rack 240 (926). The anode 210 and rack240 (including the wafer 225) are submerged in an electroplatingsolution 260 contained in an electroplating bath 250 such that theexposed portion of the metal layer 313 at the bottom surface of thetrench 335 (i.e., the cathode 220) is exposed to the electroplatingsolution 260 (928). Next, current flow from the power supply through thecurrent path (i.e., through the rack 240, through back side contact 226,through the electrical connector 370, through any interconnect316/intermediate metal layers 311-313, through the top metal layer 313to the exposed portion of the metal layer at the bottom surface of thetrench 335 (i.e., to the cathode 220) is selectively controlled (e.g.,by either the electrical connector 370 (in the case of an in-substrateswitch) or by the power supply 290 itself (in the case of anin-substrate simple ohmic path) (930). Selective control of current flowand, thereby, electron flow through this current path causes metal oralloy ions metal or alloy ions in the electroplating solution 260 tolose their charge and to electroplate the feature 700 onto the bottomsurface of the trench 335 (i.e., onto cathode 220). This process can berepeated with different electroplating solutions and/or anodes to createdifferent layers of electroplated material (e.g., layers 701-703 offeature 700) within the trench 335.

Once the desired feature 700 is electroplated into the trench 335, themask 1200 covering the additional via/contact holes 1100 can be removed(932) and standard via interconnects/contacts 1101 can be formed therein(934, see FIG. 16). As discussed above, for plating of the standard viainterconnects/contact 1101 to occur current must flow to the metal layer1102 at the bottom surface of the additional via/contact holes 1101.This current flow can be established through the use of any number ofknown techniques or structures (not shown). For example, current fromthe power source can flow across the wafer substrate generally.Alternatively, wire 1102 can be electrically connected to the powersource by way of a second backside contact or by an electricalconnection to any one of wires 311, 312, 313. Standard via interconnectformation can be followed by next metal layer 1701 and next ILD layerformation 1702, etc., to complete BEOL wafer processing (936, see FIG.17).

Thus, the electroplating method, discussed above, can be used toelectroplate any number of various different types of features on thewafer 225, including but not limited to, back end of the line (BEOL)conductors, insulators, metal-insulator-metal (MIM) structures,capacitors, anti-fuse devices, etc. In one particular embodiment, thiselectroplating method can be used when forming one or more anti-fuselayers 701-703 of a BEOL in-via hole or in-contact hole anti-fuse device700 on the semiconductor wafer 225 (as illustrated in FIG. 7 and furthercan be used when programming this BEOL anti-fuse device 700.

More specifically, FIG. 10 is a flow diagram illustrating an embodimentof the method of FIG. 7 used particularly for forming the BEOL anti-fusedevice 700 of FIG. 7 and for programming that BEOL anti-fuse device 700.Specifically, to accomplish this, the wafer 225 is first processed asdescribed above in process steps 902-920 of FIG. 9. That is, a contactis formed within and at the back side of the wafer substrate (905). Anelectrical connector is formed within the substrate adjacent to thecontact (906). A metal layer is formed on the front side of thesubstrate adjacent to the electrical connector (908). A dielectric layeris formed on the metal layer (914). A trench is formed in the dielectriclayer so as to expose a portion of the metal layer at the bottom surfaceof the trench (916). Then, the BEOL anti-fuse device 700 is formed byforming a plurality of anti-fuse layers 701-703 in the trench 335.Specifically, referring to FIG. 10, when forming a BEOL anti-fuse device700, the wafer 225 is place in an electroplating rack such that the backside contact 226 and also wire 376 (if the electrical connector 370 isan in-substrate field effect transistor, as illustrated in FIG. 4 a) areelectrically connected to the rack 240 (1002, see FIG. 2). The rack 240and an anode 210 are electrically connected to a power supply 290(1004).

Next, a first electrodepositon process is performed (1006-1008, see FIG.13). This first electrodeposition process can comprise submerging theanode 210 and rack 240 (including the wafer 225) in a firstelectroplating solution 1361 in an electroplating bath such that theexposed portion of the metal layer 313 at the bottom surface of thetrench (i.e., the cathode 220) is exposed to the first electroplatingsolution 1361 (1006). During this first electrodeposition process,current flow and, thereby, electron flow through the current path 385from the power supply 290 to the exposed portion of the metal layer 313at the bottom surface of the trench (i.e., to the cathode) isselectively controlled (e.g., by either the electrical connector 370 (inthe case of an in-substrate switch) or by the power supply itself (inthe case of an in-substrate simple ohmic path) to electroplate a firstanti-fuse layer 701 onto the bottom surface of the trench 335 (1008, seeFIG. 3 b).

After the first anti-fuse layer 501 is electroplated onto the bottomsurface of the trench 335, a second electrodepostion process can beperformed (1010-1012, see FIG. 14). This second electrodepositionprocess can comprise removing the first electroplating solution 1361from the electroplating bath and replacing it with a secondelectroplating solution 1362 (1010). During this secondelectrodeposition process, current flow and, thereby, electron flowthrough the current path 385 is selectively controlled (e.g., by eitherthe electrical connector 370 (in the case of an in-substrate switch) orby the power supply itself (in the case of an in-substrate simple ohmicpath) to electroplate a second anti-fuse layer 702 onto the firstanti-fuse layer 701 within the trench 335 (1012, see FIG. 3 b).Specifically, current flow is selectively controlled, during this secondelectrodeposition process, so that that the second anti-fuse layer willbe approximately 100-500 angstroms (Å) thick.

After the second anti-fuse layer 701 is plated onto the first anti-fuselayer 702 at process 1012, a third electrodepositon processes can beperformed (1014-1016, see FIG. 15). This third electrodeposition processcan comprise removing the second electroplating solution 1362 from theelectroplating bath and replacing it with a third electroplatingsolution 1363 (1014). During this third electrodeposition process,current flow and, thereby, electron flow through the current path 385 isselectively controlled (e.g., by either the electrical connector 370 (inthe case of an in-substrate switch) or by the power supply itself (inthe case of an in-substrate simple ohmic path) to electroplate a thirdanti-fuse layer 703 onto the second anti-fuse layer 702 within thetrench 335 (1016, see FIG. 3 b).

Again, once the electroplating processes are completed, the rack 240 canbe removed from the electroplating bath, the wafer 225 can be removedfrom the rack 240 and the mask 1200 can be removed from the wafer 225(1018). Then, standard via interconnect/contact processing can beperformed in order to form standard via interconnects/contacts 1101, asnecessary, in any unmasked hole 1100 and to fill any remaining unfilledportion of trench 335 (1020, see FIG. 16). As discussed above, forplating of the standard via interconnects/contact 1101 to occur currentmust flow to the metal layer 1102 at the bottom surface of theadditional via/contact holes 1101. This current flow can be establishedthrough the use of any number of known techniques or structures (notshown). For example, current from the power source can flow across thewafer substrate generally. Alternatively, wire 1102 can be electricallyconnected to the power source by way of a second backside contact or byan electrical connection to any one of wires 311, 312, 313. Standard viainterconnect processing can be followed by standard next level metal1701 and ILD 1702 formation, etc., to complete BEOL wafer processing(1026, see FIG. 17).

Alternatively, after the second anti-fuse layer 702 is plated onto thefirst anti-fuse layer 701 at process 1012, the rack 240 can be removedfrom the bath 250, the wafer 225 can be removed from the rack 240 andthe mask 1200 can be removed from the wafer 225 (1022, see FIG. 18).Then, a third anti-fuse layer 703 can be formed on the second anti-fuselayer 702 within the trench 335 simultaneously with forming at least onestandard via interconnect 1101 or contact in an additional trench 1100(i.e., in an additional via hole or contact hole) on the wafer 225(1024, see FIG. 19). For example, after removing the mask 1200 from thewafer 225, the wafer 225 can be returned to the rack 240 and the rack240 can be returned to the bath 250. The second electroplating solutioncan be replaced with a third electroplating solution. The wafer 225 isheld in the third electroplating solution in the electroplating bathsuch that the second anti-fuse layer and additional unmasked trench 1100are exposed to the third electroplating solution. As discussed above,for plating of the standard via interconnects/contact 1101 to occurcurrent must flow to the metal layer 1102 at the bottom surface of theadditional via/contact holes 1101. This current flow can be establishedthrough the use of any number of known techniques or structures (notshown). For example, current from the power source can flow across thewafer substrate generally. Alternatively, wire 1102 can be electricallyconnected to the power source by way of a second backside contact or byan electrical connection to any one of wires 311, 312, 313.

The above described method steps of FIG. 10 can be used to form a BEOLanti-fuse device 700 in which the first anti-fuse layer 701 comprisestitanium nitride (TiN), the second anti-fuse layer 702 comprises silicondioxide (SiO₂) and the third anti-fuse layer 703 comprises copper. Thatis, the particular method steps for forming an exemplary BEOL anti-fusedevice can comprise first forming a titanium nitride (TiN) layer 701 onthe bottom surface 220 of the trench by performing a firstelectrodeposition process (1006-1008). Next, a silicon dioxide (SiO₂)layer 702 can be formed on the titanium nitride (TiN) layer 701 by usinga second electrodeposition process (1010-1012). Finally, a copper layer703 can be formed on the silicon dioxide (SiO₂) layer 702 by usingeither a third electrodeposition process (1014-1016) or a standard viainterconnect formation process (1022-1024).

As mentioned above, only upon programming at subsequent process step1028 (i.e., by applying a current above a specified limit) does ananti-fuse device 700 provide a low resistance electrical connection dueto migration of metal ions into the second anti-fuse layer 702. The BEOLanti-fuse device configuration (i.e., TiN—SiO₂—Cu) resulting from theseexemplary method steps provides the added benefit of allowing for copperion (Cu++) assist during anti-fuse programming. However, when formingthe anti-fuse device 700, alternative anti-fuse conductive elements caninclude, but are not limited to, nickel (Ni), cobalt (Co), iron (Fe),copper (Cu), platinum (Pt) and rehium (Re).

It should be noted that it is important in semiconductor waferprocessing to have inherent knowledge regarding the functionality of ananti-fuse (e.g., the functionality of the anti-fuse device 700,discussed in detail above, or for that matter an eFuse) once the waferfabrication is complete. Having such apriori knowledge is an enablingfeature of these electrical fuses. Specifically, various circuits withina chip (e.g., input-output blocks, memory bits, etc.) have redundantspares built into the chip. These spares can be used to non-functionalcircuits (e.g., non-functional input-output blocks, non-functionalmemory elements, etc.). Electrical fuses do not have such an option.Since an electrical anti-fuse is initially open and then duringprogramming is closed, the two possible states of the anti-fuse cancause a permanent error in the anti-fuse use if a fabrication faultcauses the anti-fuse to be stuck in one state or the other. The samesituation exists for an eFuse; except that in the case of an eFuse theunprogrammed fuse is normally shorted, and after programming the eFuseis normally open. That is, if errors (e.g., lithographic patterningerrors or fill errors) occur during prior art anti-fuse devicefabrication and these errors result in a faulty anti-fuse device, thenknowledge of the faulty device may not be known until after the productis in use and programming is attempted. However, with the anti-fuseformation method illustrated in FIG. 10 and described in detail above,electron flow can be monitored at each of the electrodeposition stagesof fabrication (e.g., see steps 1008, 1012, 1016, etc.) to determine ifplating has occurred and, thereby, to guarantee formation of theanti-fuse device structure. Such guaranteed formation is both anecessary and sufficient condition for anti-fuse enablement because itelectrically guarantees 100% pre-programming yield. Again, 100%pre-programming yield was not possible with prior fabrication techniquesbecause knowledge of the faulty device could not occur until programmingwas attempted. As such, the present method for forming an anti-fusedevice minimizes or eliminates products being sent to customers withfaulty anti-fuse devices that can not be programmed. That is, theabove-described technique of forming an electroplated anti-fuse or eFusewith electron flow feedback ensures proper fabrication and maximizesunprogrammed yield.

Referring again to FIG. 10, once the BEOL anti-fuse device 700 is formedand the BEOL wafer processing is completed, the BEOL anti-fuse device700 can be programmed by selectively controlling current flow throughthe current path in the same manner as described above forelectrodeposition (1028). That is, referring to FIG. 8, a current path885 can be established form a power supply 890 through the back sidecontact, through the electrical connector 370, through the metal layer313 to the BEOL anti-fuse device 700 within the trench. Then, currentflow through this current path 885 can be selectively controlled (e.g.,by either the electrical connector 370 (in the case of an in-substrateswitch) or the power supply 890 itself (in the case of a simple ohmicpath) in order to apply a current above a specified limit to theanti-fuse device 700 and, more particularly to the first anti-fuse layer702 adjacent to the bottom surface of the trench. This applied currentwill cause metal ions to migrate into the second anti-fuse layer 701,thereby, reducing resistance across the anti-fuse device 700 (i.e.,thereby, programming the anti-fuse device 700).

Therefore, disclosed above are embodiments of a circuit and method forelectroplating a feature, such as a back end of the line (BEOL)anti-fuse device, onto a semiconductor wafer. The electroplating circuitand method embodiments eliminate the use of a seed layer and, thereby,minimize subsequent processing steps (e.g., etching or chemicalmechanical polishing (CMP)). Specifically, the circuit and methodembodiments allow for selective electroplating of one or more metal oralloy materials onto an exposed portion of a metal layer in a trench onthe front side of a semiconductor substrate. This is accomplished byproviding a unique wafer structure that allows a current path to beestablished from a power supply through a back side contact andin-substrate electrical connector to the metal layer. Duringelectrodeposition, current flow and, thereby, electron flow, through thecurrent path can be selectively controlled. Additionally, if theelectroplated feature is an anti-fuse device, current flow through thiscurrent path can also be selectively controlled in order to program theanti-fuse device.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationssuch specific embodiments without departing from the generic concept,and, therefore, such adaptations and modifications should and areintended to be comprehended within the meaning and range of equivalentsof the disclosed embodiments. It is to be understood that thephraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the invention hasbeen described in terms of embodiments, those skilled in the art willrecognize that these embodiments can be practiced with modificationwithin the spirit and scope of the appended claims.

1. A circuit structure comprising: a wafer comprising: a substratehaving a front side and a backside; a contact at said back side of saidsubstrate; an electrical connector within said substrate adjacent saidcontact; a metal layer on said front side of said substrate adjacentsaid electrical connector, wherein said electrical connector is adaptedto provide an electrical connection between said contact and said metallayer; and a dielectric layer on said metal layer; and a trench in saiddielectric layer, wherein an entire bottom surface of said trenchcomprises a portion of said metal layer, wherein said contact is adaptedto connect to a power supply such that a current path is establishedfrom said power supply through said back side contact, said electricalconnector and said metal layer to said bottom surface of said trench,wherein said power supply is adapted to pass a current through saidcurrent path and wherein one of said electrical connector and said powersupply are adapted to selectively control flow of said current throughsaid current path.
 2. The circuit structure of claim 1, wherein saidelectrical connector comprises a switch and wherein said switch isadapted to selectively control said flow so as to at least one of:electroplate a feature onto said bottom surface of said trench, andprogram an anti-fuse device on said bottom surface of said trench. 3.The circuit structure of claim 1, wherein said electrical connectorcomprises a simple ohmic path and wherein said power supply is adaptedto selectively control said flow so as to at least one of: electroplatea feature onto said bottom surface of said trench, and program ananti-fuse device on said bottom surface of said trench.
 4. The circuitstructure of claim 1, further comprising a rack electrically connectedto said power supply, wherein said rack is adapted to hold said wafer inan electroplating solution such that said bottom surface of said trenchis exposed to said electroplating solution and wherein said rack isfurther adapted to electrically connect said back side contact to saidpower supply.
 5. A circuit structure comprising: a wafer comprising: asubstrate having a front side and a back side; a contact at said backside of said substrate an electrical connector within said substrateadjacent said contact; a metal layer on said front side of saidsubstrate adjacent said electrical connector, wherein said electricalconnector is adapted to provide an electrical connection between saidcontact and said metal layer; and a dielectric layer on said metallayer; and a trench in said dielectric layer, wherein an entire bottomsurface of said trench comprises a portion of said metal layer, whereinsaid contact is adapted to connect to a power supply such that a currentpath is established from said power supply through said back sidecontact, said electrical connector and said metal layer to said bottomsurface of said trench, wherein said power supply is adapted to pass acurrent through said current path and wherein one of said electricalconnector and said power supply are adapted to selectively control flowof said current through said current path, wherein said electricalconnector comprises a switch and wherein said switch is adapted toselectively control said flow so as to at least one of: electroplate afeature onto said bottom surface of said trench, and program ananti-fuse device on said bottom surface of said trench.
 6. The circuitstructure of claim 5, wherein said electrical connector comprises asimple ohmic path and wherein said power supply is adapted toselectively control said flow so as to at least one of: electroplate afeature onto said bottom surface of said trench, and program ananti-fuse device on said bottom surface of said trench.
 7. The circuitstructure of claim 5, further comprising a rack electrically connectedto said power supply, wherein said rack is adapted to hold said wafer inan electroplating solution such that said bottom surface of said trenchis exposed to said electroplating solution and wherein said rack isfurther adapted to electrically connect said back side contact to saidpower supply.